1. Field of the Invention
The present invention relates to a transport method and a transport apparatus for a semiconductor wafer (hereinafter, also referred to as a “wafer” for short).
2. Description of the Related Art
Generally, the following procedure has been adopted. In grinding (back grinding) of the back surface of a wafer having been finished with a pattern forming processing, for example, a protective tape is applied to the front surface of the wafer in advance and, also, a portion of the protective tape extending out from the wafer periphery is also cut off. Moreover, the wafer the front surface of which is all protected with the protective tape is suction-held by a sucking disc at the front surface thereof and subjected to grinding and, thereafter, the back surface thereof is suction-held at part thereof to change places of the wafer and transfer to various processing tables.
In recent years, there has been a tendency that a wafer thickness after grinding the back surface of a wafer is thinner and thinner. As a result of the tendency, a rigidity of a wafer itself thus ground to be thinner is reduced, thereby generating a warp in the wafer even with a slight stress generated in a surface thereof.
A wafer with such a warp, when being transferred while part of a front or back surface thereof is suction-held, suffers deficiency in vacuum suction and shifts its position during transfer, leading to an inconvenience to disable the transfer to have a stably high accuracy. Hence, the front or back surface of a wafer has been held by vacuum suction using an area nearly as large as the whole of the front or back surface thereof when being held with a wafer holding means such as an alignment stage or a wafer chuck table.
In recent years, however, the front and back surfaces of a wafer have been brought into contact with a wafer holding means such as an alignment stage or a wafer chuck table at nearly the whole surface areas of the wafer; therefore, dust (foreign matter) generated by the contact are conspicuously accumulated on the wafer holding means and dust attached to a wafer increases with a rise in the number of handled other wafers, which has resulted in occurrence of defective products, and in turn in reduction in production yield.